Restricted accessBrief reportFirst published online 2021-11
Cells Stimulated with More Than One Toll-Like Receptor–Ligand in the Presence of a MyD88 Inhibitor Augmented Interferon- β via MyD88-Independent Signaling Pathway
Host exposure to pathogens engage multiple pathogen recognition receptors (PRRs) including toll-like receptors (TLRs); recruit intracellular signaling adaptor proteins primarily myeloid differentiation primary response protein 88 (MyD88) for activating downstream signaling cascades, which culminate in the production of type I interferons (IFNs), proinflammatory cytokines, and chemokines; and impede pathogen replication and dissemination. However, recent studies highlight that absence of MyD88 increased antiviral type I IFN induction, and MyD88−/− mice showed a higher survival rate compared with the low survival rate of the MyD88+/+ mice, implicating MyD88 limits antiviral type I IFN response. As a single infectious agent may harbor multiple PRR agonists, which trigger different sets of TLR-initiated immune signaling, we examined whether MyD88 inhibition during stimulation of cells with more than one TLR–ligand would augment type I IFN. We stimulated human U87- and TLR3-transfected HEK293–TLR7 cells with TLR–ligands, such as lipopolysaccharides (LPS) (TLR4–ligand) plus poly I:C (TLR3–ligand) or imiquimod (R837, TLR7–ligand) plus poly I:C, in the presence of compound 4210, a previously reported MyD88 inhibitor, and measured IFN-β response using an enzyme-linked immunosorbent assay. Our results showed that when U87- or TLR3-transfected HEK293–TLR7 cells were stimulated with TLR–ligands, such as poly I:C plus LPS or poly I:C plus R837, IFN-β production was significantly increased with MyD88 inhibition in a dose-dependent manner. Collectively, these results indicate that during more than one TLR–ligand-induced immune signaling event, impairment of antiviral type I IFN response was restored by inhibition of MyD88 through MyD88-independent pathway of type I IFN signaling, thus, offer a MyD88-targeted approach for type I IFN induction.
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